Scissor lift descent control systems and methods

ABSTRACT

A lift device comprises a base, a retractable lift mechanism, a work platform, a linear actuator, and a descent control mechanism. The base has a plurality of wheels. The retractable lift mechanism has a first end coupled to the base and is moveable between an extended position and a retracted position. The work platform is configured to support a load. The work platform is coupled to and supported by a second end of the retractable lift mechanism. The linear actuator is configured to selectively move the retractable lift mechanism between the extended position and the retracted position. The linear actuator has an electric motor. The descent control mechanism is configured to reduce a speed at which the retractable lift mechanism is moved from the extended position to the retracted position.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No. 62/830,164, filed Apr. 5, 2019, which is incorporated herein by reference in its entirety.

BACKGROUND

Lift devices commonly include a vertically movable platform that is supported by a foldable series of linked supports. The linked supports are arranged in an “X” pattern, crisscrossing with one another. A hydraulic cylinder generally controls vertical movement of the platform by engaging and rotating (i.e., unfolding) the lowermost set of linked supports, which in turn unfolds the remainder of the series of linked supports within the system. The platform raises and lowers based upon the degree of actuation by the hydraulic cylinder. A hydraulic cylinder may also control various other vehicle actions, such as, for example, steering or platform tilt functions. Lift devices using one or more hydraulic cylinders require an on-board reservoir tank to store hydraulic fluid for the lifting process.

SUMMARY

One exemplary embodiment relates to a lift device. The lift device comprises a base, a retractable lift mechanism, a work platform, a linear actuator, and an electromagnetic brake. The base has a plurality of wheels. The retractable lift mechanism has a first end coupled to the base and is moveable between an extended position and a retracted position. The work platform is configured to support a load. The work platform is coupled to and supported by a second end of the retractable lift mechanism. The linear actuator is configured to selectively move the retractable lift mechanism between the extended position and the retracted position. The linear actuator has an electric motor. The electromagnetic brake is coupled to the linear actuator and movable between an engaged position, in which the retractable lift mechanism is prevented from moving between the extended position and the retracted position, and a disengaged position, in which the retractable lift mechanism is allowed to move between the extended position and the retracted position. In the event of a power failure, the electromagnetic brake is biased toward the engaged position.

Another exemplary embodiment relates to a lift device. The lift device comprises a base, a retractable lift mechanism, a work platform, a linear actuator, and a descent control mechanism. The base has a plurality of wheels. The retractable lift mechanism has a first end coupled to the base and is moveable between an extended position and a retracted position. The work platform is configured to support a load. The work platform is coupled to and supported by a second end of the retractable lift mechanism. The linear actuator is configured to selectively move the retractable lift mechanism between the extended position and the retracted position. The linear actuator has an electric motor. The descent control mechanism is configured to reduce a speed at which the retractable lift mechanism is moved from the extended position to the retracted position.

Another exemplary embodiment relates to a lift device. The lift device comprises a base, a retractable lift mechanism, a work platform, a linear actuator, an electromagnetic brake, a manual release device, and a descent control mechanism. The base has a plurality of wheels. The retractable lift mechanism has a first end coupled to the base and is moveable between an extended position and a retracted position. The work platform is configured to support a load. The work platform is coupled to and supported by a second end of the retractable lift mechanism. The linear actuator is configured to selectively move the retractable lift mechanism between the extended position and the retracted position. The linear actuator has an electric motor. The electromagnetic brake is coupled to the linear actuator and movable between an engaged position, in which the retractable lift mechanism is prevented from moving between the extended position and the retracted position, and a disengaged position, in which the retractable lift mechanism is allowed to move between the extended position and the retracted position, the electromagnetic brake being biased toward the engaged position in the event of a power failure. The manual release device is configured to manually move the electromagnetic brake from the engaged position to the disengaged position. The descent control mechanism is configured to reduce a speed at which the retractable lift mechanism is moved from the extended position to the retracted position.

The invention is capable of other embodiments and of being carried out in various ways. Alternative exemplary embodiments relate to other features and combinations of features as may be recited herein.

BRIEF DESCRIPTION OF THE FIGURES

The disclosure will become more fully understood from the following detailed description, taken in conjunction with the accompanying figures, wherein like reference numerals refer to like elements, in which:

FIG. 1A is a side perspective view of a lift device in the form of a scissor lift, according to an exemplary embodiment;

FIG. 1B is another side perspective view of the lift device of FIG. 1A;

FIG. 2A is a side view of the lift device of FIG. 1A, shown in a retracted or stowed position;

FIG. 2B is a side perspective view of the lift device of FIG. 1A, shown in an extended or work position;

FIG. 3 is a side view of the lift device of FIG. 1A, depicting various vehicle controllers;

FIG. 4 is a side view of a linear actuator of the lift device of FIG. 1A;

FIG. 5 is a bottom view of the linear actuator of FIG. 4;

FIG. 6 is a side view of a push tube and a nut assembly of the linear actuator of FIG. 4;

FIG. 7A is a cross-sectional view of an electromagnetic brake of the linear actuator of FIG. 4, shown in an engaged position;

FIG. 7B is a cross-sectional view of the electromagnetic brake of FIG. 7A, shown in a disengaged position;

FIG. 8 is a perspective view of a manual pull handle of a manual pull device of the lift device of FIG. 1A;

FIG. 9 is a side perspective view of the lift device of FIG. 1A, showing the manual pull device;

FIG. 10 is a cross-sectional view of the electromagnetic brake of FIG. 7A, shown including a release tab;

FIG. 11 is a perspective view of the linear actuator of FIG. 4, showing a centrifugal brake;

FIG. 12 is a perspective view of the centrifugal brake of FIG. 11, showing the internal components of the centrifugal brake; and

FIG. 13 is a side perspective view of another lift device in the form of a boom lift, according to another exemplary embodiment.

DETAILED DESCRIPTION

Before turning to the figures, which illustrate the exemplary embodiments in detail, it should be understood that the present application is not limited to the details or methodology set forth in the description or illustrated in the figures. It should also be understood that the terminology is for the purpose of description only and should not be regarded as limiting.

Referring to the figures generally, the various exemplary embodiments disclosed herein relate to systems, apparatuses, and methods for the controlled descent of a work platform on a lift device. The lift device includes an electromagnetic brake that is configured to engage in the event of a power failure (e.g., a battery discharge or a control system failure) to hold the work platform in place (i.e., at a constant height). The lift device further includes a manual release mechanism to selectively release the electromagnetic brake to lower the work platform in the event of a battery discharge or a control system failure. The lift device further includes a descent limiting mechanism that limits the speed at which the work platform is allowed to lower when the electromagnetic brake is disengaged. Thus, the lift device allows for the work platform and any worker on the work platform to be safely lowered from a deployed work position in the event of a battery discharge or a control system failure.

According to the exemplary embodiment depicted in FIGS. 1A and 1B, a vehicle, shown as vehicle 10, is illustrated. The vehicle 10 may be a scissor lift, for example, which can be used to perform a variety of different tasks at various elevations. The vehicle 10 includes a base 12 supported by wheels 14A, 14B positioned about the base 12. The vehicle 10 further includes a battery 16 positioned on board the base 12 of the vehicle 10 to supply electrical power to various operating systems present on the vehicle 10.

The battery 16 can be a rechargeable lithium-ion battery, for example, which is capable of supplying a direct current (DC) or alternating current (AC) to controls, motors, actuators, and the like included on board the vehicle 10. The battery 16 can include at least one input 18 capable of receiving electrical current to recharge the battery 16. In some embodiments, the input 18 is a port capable of receiving a plug in electrical communication with an external power source, like a wall outlet. The battery 16 can be configured to receive and store electrical current from one of a traditional 120 V outlet, a 240 V outlet, a 480 V outlet, an electrical power generator, or another suitable electrical power source.

The vehicle 10 further includes a retractable lift mechanism, shown as a scissor lift mechanism 20, coupled to the base 12. The scissor lift mechanism 20 supports a work platform 22 (shown in FIG. 3). As depicted, a first end 23 of the scissor lift mechanism 20 is anchored to the base 12, while a second end 24 of the scissor lift mechanism 20 supports the work platform 22. As illustrated, the scissor lift mechanism 20 is formed of a foldable series of linked support members 25. The scissor lift mechanism 20 is selectively movable between a retracted or stowed position (shown in FIG. 2A) and an extended, deployed, or work position (shown in FIG. 2B) using an actuator, shown as linear actuator 26. The linear actuator 26 is an electric actuator. The linear actuator 26 controls the orientation of the scissor lift mechanism 20 by selectively applying force to the scissor lift mechanism 20. When a sufficient force is applied to the scissor lift mechanism 20 by the linear actuator 26, the scissor lift mechanism 20 unfolds or otherwise deploys from the stowed or retracted position into the work position. Because the work platform 22 is coupled to the scissor lift mechanism 20, the work platform 22 is also raised away from the base 12 in response to the deployment of the scissor lift mechanism 20.

As shown in FIG. 3, the vehicle 10 further includes a vehicle controller 27 and a lift motor controller 28. The vehicle controller 27 is in communication with the lift motor controller 28 and is configured to control various driving systems on the vehicle 10. The lift motor controller 28 is in communication with the linear actuator 26 and is configured to control the movement of the scissor lift mechanism 20. Communication between the lift motor controller 28 and the linear actuator 26 and/or between the vehicle controller 27 and the lift motor controller 28 can be provided through a hardwired connection or through a wireless connection (e.g., Bluetooth, Internet, cloud-based communication system, etc.). It should be understood that each of the vehicle controller 27 and the lift controller 28 includes various processing and memory components configured to perform the various activities and methods described herein. For example, in some instances, each of the vehicle controller 27 and the lift controller 28 includes a processing circuit having a processor and a memory. The memory is configured to store various instructions configured to, when executed by the processor, cause the vehicle 10 to perform the various activities and methods described herein.

As illustrated in the exemplary embodiment provided in FIGS. 4-6, the linear actuator 26 includes a push tube assembly 30, a gear box 32, and an electric lift motor 34. The push tube assembly 30 includes a protective outer tube 36 (shown in FIGS. 4 and 5), a push tube 38, and a nut assembly 40 (shown in FIG. 6). The protective outer tube 36 has a trunnion connection portion 42 disposed at a proximal end 44 thereof. The trunnion connection portion 42 is rigidly coupled to the gear box 32, thereby rigidly coupling the protective outer tube 36 to the gear box 32. The trunnion connection portion 42 further includes a trunnion mount 45 that is configured to rotatably couple the protective outer tube 36 to one of the support members 25 (as shown in FIG. 2B).

The protective outer tube 36 further includes an opening at a distal end 46 thereof. The opening of the protective outer tube 36 is configured to slidably receive the push tube 38. The push tube 38 includes a connection end, shown as trunnion mount 48, configured to rotatably couple the push tube 38 to another one of the support members 25 (as shown in FIG. 2B). As will be discussed below, the push tube 38 is slidably movable and selectively actuatable between an extended position (shown in FIG. 2B) and a retracted position (shown in FIG. 4).

Referring now to FIG. 6, the push tube 38 is rigidly coupled to the nut assembly 40, such that motion of the nut assembly 40 results in motion of the push tube 38. The push tube 38 and the nut assembly 40 envelop a central screw rod. The central screw rod is rotatably engaged with the gear box 32 and is configured to rotate within the push tube 38 and the nut assembly 40, about a central axis of the push tube assembly 30. The nut assembly 40 is configured to engage the central screw rod and translate the rotational motion of the central screw rod into translational motion of the push tube 38 and the nut assembly 40, with respect to the central screw rod, along the central axis of the push tube assembly 30. In some embodiments, the nut assembly 40 may be, for example, a ball screw assembly or a roller screw assembly. In some other embodiments, the nut assembly 40 may be any other suitable assembly for translating rotational motion of the central screw rod into translational motion of the push tube 38 and the nut assembly 40.

Referring again to FIG. 4, the lift motor 34 is configured to selectively provide rotational actuation to the gear box 32. The rotational actuation from the lift motor 34 is then translated through the gear box 32 to selectively rotate the central screw rod of the push tube assembly 30. The rotation of the central screw rod is then translated by the nut assembly 40 to selectively translate the push tube 38 and the nut assembly 40 along the central axis of the push tube assembly 30. Accordingly, the lift motor 34 is configured to selectively actuate the push tube 38 between the extended position and the retracted position. Thus, with the trunnion mount 45 of the protective outer tube 36 and the trunnion mount 48 of the push tube 38 each rotatably coupled to their respective support members 25, the lift motor 34 is configured to selectively move the scissor lift mechanism 20 to various heights between and including the retracted or stowed position and the deployed or work position.

The lift motor 34 may be an AC motor (e.g., synchronous, asynchronous, etc.) or a DC motor (shunt, permanent magnet, series, etc.). In some instances, the lift motor 34 is in communication with and powered by the battery 16. In some other instances, the lift motor 34 may receive electrical power from another electricity source on board the vehicle 10.

As depicted in the exemplary embodiment shown in FIGS. 7A and 7B, the lift motor 34 includes an electromagnetic brake 50 configured to hold the work platform 22 in place (i.e., at a constant height) in the case of a battery discharge or a control system failure. As illustrated in FIGS. 7A and 7B, the electromagnetic brake 50 includes a pressure plate 52, a friction disk 54, an armature 56, a magnetic body 58, and a wire coil 60. As illustrated, the pressure plate 52 is disposed at a first end 62 of the electromagnetic brake 50. The pressure plate 52 surrounds a hub 64. The hub 64 is fixed to a rotor 66 of the lift motor 34, such that the hub 64 and the rotor 66 are rotationally coupled (e.g., rotation of one of the hub 64 and the rotor 66 results in the rotation of the other of the hub 64 and the rotor 66). The friction disk 54 is disposed adjacent the pressure plate 52. The friction disk 54 is fixed to the hub 64, such that of the hub 64, the rotor 66, and the friction disk 54 are all rotationally coupled (e.g., rotation of one of the hub 64, the rotor 66, and the friction disk 54 results in the rotation of the other two of the hub 64, the rotor 66, and the friction disk 54). The armature 56 is disposed adjacent the friction disk 54, and is biased into contact with the friction disk 54 by engagement springs 68.

The magnetic body 58 and the wire coil 60 are disposed at a second end 70 of the electromagnetic brake 50. The magnetic body 58 and the wire coil 60 are configured to selectively produce a magnetic force on the armature 56 to pull the armature 56 toward the magnetic body 58.

Referring now to FIG. 7A, the electromagnetic brake 50 is shown in an engaged position. Specifically, when there is no power applied to the wire coil 60 of the lift motor 34, the magnetic body 58 and the wire coil 60 do not produce any magnetic force on the armature 56. As such, the engagement springs 68 bias the armature 56 against the friction disk 54, thereby preventing rotation of the friction disk 54. Because the friction disk 54 is fixed to the hub 64, and the hub is rigidly coupled to the rotor 66, the rotor 66 is also prevented from rotating, thereby preventing the work platform 22 from moving vertically (e.g., because the central screw rod is prevented from spinning, such that the linear actuator is prevented from translating). Accordingly, when no power is applied to the wire coil 60 of the lift motor 34, the electromagnetic brake 50 is biased toward the engaged position.

Referring now to FIG. 7B, the electromagnetic brake 50 is shown in a disengaged position. Specifically, when power (e.g., a current) is applied to the wire coil 60 of the lift motor 34, the magnetic body 58 and the wire coil 60 produce an electromagnetic force on the armature 56, compressing the engagement springs 68 and pulling the armature 56 out of contact with the friction disk 54. Accordingly, the friction disk 54, the hub 64, and the rotor 66 are all free to rotate. As such, the lift motor 34 is allowed to function normally.

During normal operation, when the lift motor 34 is commanded to lift or lower the work platform 22, power is also applied to the wire coil 60 to allow for the lift motor 34 to function as intended. Then, when the lift motor 34 is not being commanded to lift or lower the work platform 22, power is not applied to the wire coil 60, such that the friction disk 54 is engaged by the armature 56, and the work platform 22 is prevented from moving vertically.

As such, in the event of a power failure (e.g., the battery 16 is discharged or the control system fails), when power is cut from the wire coil 60, the electromagnetic brake 50 is configured to automatically return to the engaged position, and the scissor lift mechanism 20 is prevented from moving between the extended position and the retracted position. In some embodiments, if the battery 16 is discharged or the control system fails when the scissor lift mechanism 20 is in the extended position (i.e., the work platform 22 is in a raised position) it may be desired to allow for the work platform 22 (and any users working on the work platform 22) to be safely lowered from the raised or deployed position back down to the stowed or lowered position.

Accordingly, as illustrated in the exemplary embodiment shown in FIGS. 8-12, the vehicle 10 further includes a manual release device 72 and a descent limiting mechanism, shown as centrifugal brake 74. The manual release device 72 is configured to manually move the electromagnetic brake 50 into the disengaged position, such that the work platform 22 can be lowered due to gravity. The centrifugal brake 74 is configured to provide resistance to and modulate (e.g., mechanically reduce) the speed at which the work platform 22 is lowered.

Specifically, the manual release device 72 includes a manual pull handle 76 (shown in FIGS. 8 and 9) that is connected to a release tab 78 (shown in FIG. 10) through a Bowden cable 80 (shown in FIG. 9). As the manual pull handle 76 is pulled, the Bowden cable 80 pulls on the release tab 78, which is fixed to the armature 56. Accordingly, the armature 56 is moved out of contact with the friction disk 54, thereby manually moving the electromagnetic brake 50 into the disengaged position and allowing the work platform 22 to lower.

The centrifugal brake 74 is configured to modulate (e.g., mechanically reduce) the speed at which the rotor 66 is allowed to rotate. Specifically, the centrifugal brake 74 prevents the work platform 22 from descending too rapidly when the electromagnetic brake 50 is disengaged. Specifically, as best shown in FIG. 12, the centrifugal brake 74 includes a rotor connection portion 82, a pair of weights 84, a pair of retention springs 86, and a casing 88. The rotor connection portion 82 is rotationally fixed to the rotor 66 (e.g., through a keyway connection, a set screw, or any other suitable connection). The pair of weights 84 are disposed on opposite sides of the rotor connection portion 82. The pair of weights 84 are configured to engage the rotor connection portion 82, such that rotation of the rotor connection portion 82 results in rotation of the pair of weights 84, and vice versa. Each weight 84 of the pair of weights 84 includes a frictional outer surface 90. The pair of retention springs 86 are configured to maintain an inwardly-biased force on the pair of weights 84, generally directed toward the rotor 66.

During operation, as the rotor 66 rotates, the pair of weights 84 tend to move radially outward, away from the rotor 66. The pair of retention springs 86 are configured to provide a radially-inward (i.e., toward the rotor 66) force onto the weights 84, preventing the frictional outer surface 90 of the weights 84 from contacting a frictional inner surface 92 of the casing 88, and thus from reducing the rotational speed of the rotor 66, until the rotor 66 exceeds a predetermined rotational speed. That is, in some embodiments, the centrifugal brake 74 is configured to reduce the rotational speed of the rotor 66 once the rotational speed of the rotor 66 reaches or exceeds the predetermined rotational speed.

In some embodiments, the predetermined rotational speed may be approximately 2050 rpm. In some other embodiments, the predetermined rotational speed may be between 1850 rpm and 2250 rpm. In yet some other embodiments, the predetermined rotational speed may be more than 2250 rpm or less than 1850 rpm, as desired for a given application. Once the rotor 66 exceeds the predetermined rotational speed, the required centripetal force needed to retain the weights adjacent the rotor connection portion 82 exceeds the spring force, allowing the weights to move radially outward. As such, the frictional outer surface 90 of the weights 84 contacts the frictional inner surface 92 of the casing 88, which effectively limits the rotational speed of the rotor 66.

As such, during operation, in the event that the battery 16 is discharged or the control system fails, the manual release device 72 and the centrifugal brake 74 allow for the work platform 22 to be safely lowered from the deployed position. Further, in the event that the manual pull handle 76 is pulled during normal operation, the lift motor controller 28 may be configured to control the descent of the work platform 22 using the lift motor 34.

Although the illustrated centrifugal brake 74 is shown opposite the gear box 32 from the lift motor 34, in some embodiments, the centrifugal brake 74 may alternatively be located between the gear box 32 and the lift motor 34. In some other embodiments, the centrifugal brake 74 may be alternatively located opposite the electromagnetic brake 50 from the lift motor 34.

Further, in some embodiments, the descent limiting mechanism may be replaced by various other types of brake mechanisms that are configured to limit the rotational speed of the rotor 66. For example, in some embodiments, the linear actuator 26 may alternatively or additionally include a shoe brake, a drum brake, a disk brake, or any other suitable brake mechanism, as desired for a given application.

Additionally, in some embodiments, in addition to or in place of the centrifugal brake 74, the linear actuator 26 may include a descent limiting mechanism in the form of a permanent magnet motor. The permanent magnet motor has terminals that are biased toward a shunted position, but are actively held open during normal operation. As such, in the event of the battery 16 being discharged or the control system failing, the terminals are shunted together, such that the permanent magnet motor acts like a generator. With the permanent magnet motor acting like a generator, the speed at which the rotor 66 is allowed to rotate would be effectively reduced.

In some embodiments, the lift motor 34 may be a permanent magnet motor, and may be configured to both selectively actuate the linear actuator 26, while also having terminals that are biased toward a shunted position in the case of the battery 16 being discharged or the control system failing, such that the lift motor 34 acts as a generator and reduces the speed of the rotor 66 in the case of a battery discharge or a control system failure.

Referring again to FIGS. 1A and 1B, the battery 16 can also be in communication with the vehicle controller 27, which can command the battery 16 to selectively supply electrical power to a drive motor 94 to propel the vehicle 10. The drive motor 94 may similarly be an AC motor (e.g., synchronous, asynchronous, etc.) or a DC motor (shunt, permanent magnet, series, etc.) for example, which receives electrical power from the battery 16 or other electricity source on board the vehicle 10 and converts the electrical power into rotational energy in a drive shaft. The drive shaft can be used to drive the wheels 14A, 14B of the vehicle 10 using a transmission. The transmission can receive torque from the drive shaft and subsequently transmit the received torque to a rear axle 96 of the vehicle 10. Rotating the rear axle 96 also rotates the rear wheels 14A on the vehicle 10, which propels the vehicle 10.

The rear wheels 14A of the vehicle 10 can be used to drive the vehicle, while the front wheels 14B can be used to steer the vehicle 10. In some embodiments, the rear wheels 14A are rigidly coupled to the rear axle 96, and are held in a constant orientation relative to the base 12 of the vehicle 10 (e.g., approximately aligned with an outer perimeter 98 of the vehicle 10). In contrast, the front wheels 14B are pivotally coupled to the base 12 of the vehicle 10. The wheels 14B can be rotated relative to the base 12 to adjust a direction of travel for the vehicle 10. Specifically, the front wheels 14B can be oriented using an electrical steering system 100. In some embodiments, the steering system 100 may be completely electrical in nature, and may not include any form of hydraulics.

It should be appreciated that, while the retractable lift mechanism included on vehicle 10 is a scissor lift mechanism, in some instances, a vehicle may be provided that alternatively includes a retractable lift mechanism in the form of a boom lift mechanism. For example, in the exemplary embodiment depicted in FIG. 13, a vehicle, shown as vehicle 210, is illustrated. The vehicle 210 includes a retractable lift mechanism, shown as boom lift mechanism 220. The boom lift mechanism 220 is similarly formed of a foldable series of linked support members 225. The boom lift mechanism 220 is selectively movable between a retracted or stowed position and a deployed or work position using a plurality of actuators 226. Each of the plurality of actuators 226 is a linear actuator similar to the linear actuator 26.

It should be further appreciated that the linear actuators used in the lift mechanism 20, 220, as well as in the steering system 100, may be incorporated into nearly any type of electric vehicle. For example, the electric systems described herein can be incorporated into, for example, a scissor lift, an articulated boom, a telescopic boom, or any other type of aerial work platform.

Advantageously, vehicles 10, 210 may be fully-electric lift devices. All of the electric actuators and electric motors of vehicles 10, 210 can be configured to perform their respective operations without requiring any hydraulic systems, hydraulic reservoir tanks, hydraulic fluids, engine systems, etc. That is, both vehicles 10, 210 may be completely devoid of any hydraulic systems and/or hydraulic fluids generally. Said differently, both vehicles 10, 210 may be devoid of any moving fluids. Traditional lift device vehicles do not use a fully-electric system and require regular maintenance to ensure that the various hydraulic systems are operating properly. As such, the vehicles 10, 210 may use electric motors and electric actuators, which allows for the absence of combustible fuels (e.g., gasoline, diesel) and/or hydraulic fluids. As such, the vehicles 10, 210 may be powered by batteries, such as battery 16, that can be re-charged when necessary.

Although this description may discuss a specific order of method steps, the order of the steps may differ from what is outlined. Also two or more steps may be performed concurrently or with partial concurrence. Such variation will depend on the software and hardware systems chosen and on designer choice. All such variations are within the scope of the disclosure. Likewise, software implementations could be accomplished with standard programming techniques with rule-based logic and other logic to accomplish the various connection steps, processing steps, comparison steps, and decision steps.

As utilized herein, the terms “approximately”, “about”, “substantially”, and similar terms are intended to have a broad meaning in harmony with the common and accepted usage by those of ordinary skill in the art to which the subject matter of this disclosure pertains. It should be understood by those of skill in the art who review this disclosure that these terms are intended to allow a description of certain features described and claimed without restricting the scope of these features to the precise numerical ranges provided. Accordingly, these terms should be interpreted as indicating that insubstantial or inconsequential modifications or alterations of the subject matter described and claimed are considered to be within the scope of the invention as recited in the appended claims.

It should be noted that the term “exemplary” as used herein to describe various embodiments is intended to indicate that such embodiments are possible examples, representations, and/or illustrations of possible embodiments (and such term is not intended to connote that such embodiments are necessarily extraordinary or superlative examples).

The terms “coupled,” “connected,” and the like, as used herein, mean the joining of two members directly or indirectly to one another. Such joining may be stationary (e.g., permanent, etc.) or moveable (e.g., removable, releasable, etc.). Such joining may be achieved with the two members or the two members and any additional intermediate members being integrally formed as a single unitary body with one another or with the two members or the two members and any additional intermediate members being attached to one another.

References herein to the positions of elements (e.g., “top,” “bottom,” “above,” “below,” “between,” etc.) are merely used to describe the orientation of various elements in the figures. It should be noted that the orientation of various elements may differ according to other exemplary embodiments, and that such variations are intended to be encompassed by the present disclosure.

The hardware and data processing components used to implement the various processes, operations, illustrative logics, logical blocks, modules and circuits described in connection with the embodiments disclosed herein may be implemented or performed with a general purpose single- or multi-chip processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, or, any conventional processor, or state machine. A processor also may be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. The memory (e.g., memory, memory unit, storage device) may include one or more devices (e.g., RAM, ROM, Flash memory, hard disk storage) for storing data and/or computer code for completing or facilitating the various processes, layers and modules described in the present disclosure. The memory may be or include volatile memory or non-volatile memory, and may include database components, object code components, script components, or any other type of information structure for supporting the various activities and information structures described in the present disclosure. According to an exemplary embodiment, the memory is coupled to the processor to form a processing circuit and includes computer code for executing (e.g., by the processor) the one or more processes described herein.

It is important to note that the construction and arrangement of the electromechanical variable transmission as shown in the exemplary embodiments is illustrative only. Although only a few embodiments of the present disclosure have been described in detail, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited. For example, elements shown as integrally formed may be constructed of multiple parts or elements. It should be noted that the elements and/or assemblies of the components described herein may be constructed from any of a wide variety of materials that provide sufficient strength or durability, in any of a wide variety of colors, textures, and combinations. Accordingly, all such modifications are intended to be included within the scope of the present inventions. Other substitutions, modifications, changes, and omissions may be made in the design, operating conditions, and arrangement of the preferred and other exemplary embodiments without departing from scope of the present disclosure or from the spirit of the appended claims. 

What is claimed is:
 1. A lift device comprising: a base having a plurality of wheels; a retractable lift mechanism having a first end coupled to the base and being moveable between an extended position and a retracted position; a work platform configured to support a load, the work platform being coupled to and supported by a second end of the retractable lift mechanism; a linear actuator configured to selectively move the retractable lift mechanism between the extended position and the retracted position, the linear actuator having an electric motor; and an electromagnetic brake coupled to the linear actuator and movable between an engaged position, in which the retractable lift mechanism is prevented from moving between the extended position and the retracted position, and a disengaged position, in which the retractable lift mechanism is allowed to move between the extended position and the retracted position; wherein, in the event of a power failure, the electromagnetic brake is biased toward the engaged position.
 2. The lift device of claim 1, wherein the electromagnetic brake includes a pressure plate, a friction disk, an armature, a magnetic body, and a wire coil, the friction disk is rotationally coupled to a rotor of the electric motor of the linear actuator and is disposed between the armature and the pressure plate, and the armature is disposed between the magnetic body and the friction disk.
 3. The lift device of claim 2, wherein, in the engaged position, the armature is biased away from the magnetic body and into contact with the friction disk by at least one engagement spring, thereby preventing rotation of the friction disk, and, in the disengaged position, a current is applied to the wire coil to produce an electromagnetic force on the armature that overcomes a spring force of the at least one engagement spring, thereby compressing the at least one engagement spring, pulling the armature out of contact with the friction disk, and allowing the rotation of the friction disk.
 4. The lift device of claim 3, further comprising a manual release device configured to manually move the electromagnetic brake from the engaged position to the disengaged position.
 5. The lift device of claim 4, wherein the manual release device comprises a manual pull handle configured to pull a release tab fixed to the armature through a Bowden cable, thereby moving the electromagnetic brake from the engaged position into the disengaged position.
 6. The lift device of claim 5, further comprising a descent control mechanism configured to reduce a speed at which the retractable lift mechanism is moved from the extended position to the retracted position.
 7. The lift device of claim 6, wherein the descent control mechanism is a centrifugal brake rotationally coupled to the rotor of the electric motor.
 8. The lift device of claim 5, wherein the electric motor of the linear actuator of is a permanent magnet motor having terminals that are biased toward a shunted position, such that, in the event of the power failure, when the electromagnetic brake is moved into the disengaged position by the manual release device and the work platform is being lowered, the permanent magnet motor acts as a generator, electromagnetically reducing a rotational speed of the rotor of the electric motor and, thereby, reducing a speed at which the retractable lift mechanism is moved from the extended position to the retracted position.
 9. A lift device comprising: a base having a plurality of wheels; a retractable lift mechanism having a first end coupled to the base and being moveable between an extended position and a retracted position; a work platform configured to support a load, the work platform being coupled to and supported by a second end of the retractable lift mechanism; a linear actuator configured to selectively move the retractable lift mechanism between the extended position and the retracted position, the linear actuator having an electric motor; and a descent control mechanism configured to reduce a speed at which the retractable lift mechanism is moved from the extended position to the retracted position.
 10. The lift device of claim 9, wherein the descent control mechanism is a centrifugal brake rotationally coupled to a rotor of the electric motor of the linear actuator.
 11. The lift device of claim 10, wherein the centrifugal brake is configured to reduce a rotational speed of the rotor once the rotor exceeds a predetermined rotational speed.
 12. The lift device of claim 11, wherein the predetermined rotational speed is between 1850 rpm and 2250 rpm.
 13. The lift device of claim 9, further comprising an electromagnetic brake coupled to the linear actuator and movable between an engaged position, in which the retractable lift mechanism is prevented from moving between the extended position and the retracted position, and a disengaged position, in which the retractable lift mechanism is allowed to move between the extended position and the retracted position.
 14. The lift device of claim 13, wherein, in the event of a power failure, the electromagnetic brake is biased toward the engaged position.
 15. The lift device of claim 14, further comprising a manual release device configured to manually move the electromagnetic brake from the engaged position to the disengaged position.
 16. The lift device of claim 15, wherein the electric motor of the linear actuator of is a permanent magnet motor having terminals that are biased toward a shunted position, such that, in the event of the power failure, when the electromagnetic brake is moved into the disengaged position by the manual release device and the work platform is being lowered, the permanent magnet motor acts as a generator, electromagnetically reducing a rotational speed of a rotor of the electric motor and, thereby, reducing the speed at which the retractable lift mechanism is moved from the extended position to the retracted position.
 17. A lift device comprising: a base having a plurality of wheels; a retractable lift mechanism having a first end coupled to the base and being moveable between an extended position and a retracted position; a work platform configured to support a load, the work platform being coupled to and supported by a second end of the retractable lift mechanism; a linear actuator configured to selectively move the retractable lift mechanism between the extended position and the retracted position, the linear actuator having an electric motor; and an electromagnetic brake coupled to the linear actuator and movable between an engaged position, in which the retractable lift mechanism is prevented from moving between the extended position and the retracted position, and a disengaged position, in which the retractable lift mechanism is allowed to move between the extended position and the retracted position, the electromagnetic brake being biased toward the engaged position in the event of a power failure; a manual release device configured to manually move the electromagnetic brake from the engaged position to the disengaged position; a descent control mechanism configured to reduce a speed at which the retractable lift mechanism is moved from the extended position to the retracted position.
 18. The lift device of claim 17, wherein the electromagnetic brake includes a pressure plate, a friction disk, an armature, a magnetic body, and a wire coil, the friction disk is rotationally coupled to a rotor of the electric motor of the linear actuator and is disposed between the armature and the pressure plate, and the armature is disposed between the magnetic body and the friction disk.
 19. The lift device of claim 18, wherein, in the engaged position, the armature is biased away from the magnetic body and into contact with the friction disk by at least one engagement spring, thereby preventing rotation of the friction disk, and, in the disengaged position, a current is applied to the wire coil to produce an electromagnetic force on the armature that overcomes a spring force of the at least one engagement spring, thereby compressing the at least one engagement spring, pulling the armature out of contact with the friction disk, and allowing the rotation of the friction disk.
 20. The lift device of claim 19, wherein the descent control mechanism is a centrifugal brake rotationally coupled to the rotor of the electric motor of the linear actuator. 